This invention relates to a data transmission system for transmitting data through a transmission path and, in particular, to a data transmission system that is capable of varying the number of lanes in a transmission path.
In the field of long-distance data transmission, the transmission speed of a method that uses a single transmission channel (also called a lane) to transmit data has reached a ceiling and lately it is difficult to enhance the transmission speed any higher. As a way to improve a communication band, technologies have been developed in which a plurality of lanes are bundled into a seemingly single link (lane bundling and deskew between lanes of a multi-lane link (multi-lane deskew)) (see, for example, JP 2006-253852 A and IEEE P802.3ba, Clause 82, “Physical Coding Sublayer (PCS) for 64B/66B, type 40 GBASE-R and 100 GBASE-R”).
JP 2006-253852 A describes a transmission method that uses a plurality of lanes. An issue to be addressed in a transmission method that uses a multi-lane link is correcting a difference in transmission distance between lanes or, in the case of an optical transmission method, correcting a difference in data arrival time which is caused by a difference in light wavelength between lanes (difference in data arrival time between lanes is hereinafter referred to as skew). Also, the number of lanes needs to be varied to suit the type of transmission medium used. In JP 2006-253852 A, a data stream is demultiplexed to be divided among a plurality of virtual lanes on a code block basis and deskew between lanes is performed each time the number of lanes is changed in a repeater, thereby making it possible to change the number of transmission lanes while keeping the transmission capacity constant.
IEEE P802.3ba describes a transmission method that uses a plurality of lanes as a standardized technology of the 100 Gb/s Ethernet. The 100 Gb/s Ethernet mentions multi-lane transmission that accomplishes a transmission rate of 100 Gbps by bundling twenty 5-Gbps virtual lanes of data. An issue to be addressed in a transmission method that uses a multi-lane link is correcting a difference in transmission distance between lanes or, in the case of an optical transmission method, correcting a difference in data arrival time which is caused by a difference in light wavelength between lanes (difference in data arrival time between lanes is hereinafter referred to as skew). Also, the number of lanes needs to be varied to suit the type of transmission medium used.
In the 100 Gb/s Ethernet, a 100-Gbps data stream is demultiplexed to be divided among twenty virtual lanes on a code block basis and the twenty virtual lanes are multiplexed and demultiplexed on a bit basis, thereby making it possible to change the number of transmission lanes while keeping the transmission capacity constant.